The invention relates to a gamma correction circuit for television, comprising a gamma corrector connected to a circuit input to which the input signal to be gamma-corrected is applied, a first superposition stage for forming a correction signal at the output thereof, this stage comprising a first input connected to the gamma correction output and a second input connected to the circuit input, the output of the first superposition stage being connected to a first input of a second superposition stage a second input of which carries a signal to be corrected, the output connected to the circuit output carrying a gamma-corrected output signal.
Such a gamma correction circuit is disclosed in German Auslegeschrift No. 17 62 353. It is described that the signal to be corrected, which is applied to the second input of the second superposition stage is the input signal appearing at the circuit input. It follows that the gamma-corrected output signal is formed from the input signal to be gamma-corrected and the adjustable gamma-determining correction signal. When the gamma adjustment is changed, the black level and the peak-white value of the output signal remain unchanged in known manner. The result is that any desired gamma correction can be adjusted between the fixed black level and the fixed peak-white value.
A problem is encountered for input signal values which exceed the peak-white value. This situation, in which input signal values exceed the peak-white value, is caused by fierce light-reflecting or flashing scene details and frequently occurs at normal scene recordings. The problem consists in that, assuming a linearly increasing input signal from black level to beyond the peak-white value, the output signal of the gamma corrector exceeds the linear input signal between black level and peak-white value and is smaller beyond the peak-white value, so that the correction signal between black level and the peak-white value enlarges the input signal, that is to say it furnishes the gamma correction but, on the contrary, reduces the input signal beyond the peak-white value. Put differently: the correction signal is positive between black level and the peak-white value and negative for values exceeding the peak-white value. For the displayed picture this means that a fierce light-reflecting or flashing scene detail is displayed with a brightness which is below, instead of above, a brightness associated with the peak-white value. This makes a strange impression on the viewer, who expects a local higher picture brightness for the scene detail but sees a markedly lower picture brightness, lower than associated with the peak-white value.